1. Field of the Invention
The present invention relates to an image-processing system for separating an image into lamellar components and vortex components and processing these components, and particularly, to a system for correctly detecting edges of an original color image, to reproduce the original color image.
It is desired to efficiently transmit and reproduce color image data of a picture or a relief formed on a wall surface, or of a curved surface of an object such as a car body. To this end, edges of an original color image are detected. Once the edges are detected, only the data of the detected edges are transmitted to the receiver, and at the receiving side, the original color image is reproduced by using the received data of edges and by using interpolation.
Accordingly, to correctly detect the edges is important.
2. Description of the Related Art
The applicant of the present application previously filed a Japanese Patent Application No. 62-133690 entitled Color Image Transmission Processing System, a Japanese Patent Application No. 63-39284 entitled Color Image Edge-detecting and Transmission Processing System, and a Japanese Patent Application No. 2-066149 entitled Scalar Data Processing System.
In the first Japanese patent application No. 62-133690, an original color image is separated into luminance components and chrominance components, and the chrominance components are separated into lamellar components that are scalar potential components and vortex components that are vector potential components. The vortex components are compressed as compact as possible for transmission, to reduce the quantity of data to transmit.
While the first Japanese patent application, No. 62-133690 detects an edge mainly using the luminance components, the second Japanese patent application, No. 63-39284 more effectively detects edges by additionally using lamellar and vortex components.
The first and the second Japanese patent applications are the original applications of priority for U.S. Pat. No. 4,908,698 issued on Mar. 13, 1990.
The third Japanese patent application No. 2-066149 is the original application of priority for U.S. Pat. No. 5,148,501 which discloses data compression and reproduction of two-dimensional scalar data.
Since the present invention relates to edge detection, the contents of the first and second of the above Japanese patent applications will first be briefly described. An embodiment of the present invention carries out similar processes.
Generally, the chrominance component is expressed by a vector V, and when the Helmholtz theory is applied to the vector V, it is noted that the vector V can be expressed as: EQU V=grad L+rot (R.multidot.K)
where L(x,y) is a scalar potential such as the luminance, and R.multidot.K is a vector potential having a direction expressed by a unit K in the direction of the Z axis.
The lamellar component is the first item, i.e., grad L, in the above expression, and the vortex component is the second item, i.e., rot (R.multidot.K), in the above expression. By detecting and transmitting an edge line of the chrominance component by detecting only divergence V and rotation V, that exceed predetermined threshold values, which are the values on the edge line of the chrominance component of the picture; the chrominance component of the color picture for every point can be reproduced by interpolation.
A similar discussion can be applied to the luminance component. For the luminance component, the vortex component rot V is zero.
As explained above, it is possible to use luminance components or chrominance components in detecting edges. Since the reproduction of the color image is effected by using the detected edges, it it important to correctly detect the edges even when the degree of change in the chrominance components or the luminance components is small. Conventionally, since the detected edges are directly used for reproduction of the original image, the precision of the reproduced image is not good.